1. Field of the Invention
The present invention relates to an abnormal current cutoff circuit for creating a circuit break when an abnormal current flows in a circuit such as a print head driver circuit for a printer.
1. Description of the Related Art
Conventionally, when a load was being driven, abnormal currents would be detected by a current detector set up across a load. The operation of a thyristor which is connected across the poles of the power supply which receive this output is then used to blow a fuse in the power supply line.
Problems Sought to be solved by the Invention
Conventional devices however, cannot cutoff the circuit for low abnormal currents as they cannot detect abnormal currents which do not exceed the current flow present during normal operation. This means they are not sufficiently safe.
For example, when using items such as printers, a larger current is required to print solidly than a current required to print normal characters, so that the amount of current used to move the print head must be changed according to the print data for the printer. This means that if an abnormal current flows at the time of printing normal characters which does not exceed the current required to print solidly then this abnormal current cannot be detected. This can cause excess heat to be generated and in a worst case scenario can cause fire. Also, as this requires a current detector means and electrical parts such as a large current thyristor to ensure that the fuse can be blown, this approach invites cost-up.
It is, therefore, the object of this invention to provide an abnormal current circuit breaker which reliably detects abnormal currents and then cuts off the power supply, has an improved degree of safety and is of a cheaper construction.